Research On Directed Energy Deposition Process And Forming Properties For Complex Geometry Features

State-of-the-art directed energy deposition(DED)promises to provide a new process idea for manufacturing thin-walled parts with complex geometric features such as blades.How to quickly fabricate blades with better formed quality and mechanical properties has always been the focus of previous research.Based on the process of directional energy deposition,this paper combines modeling calculations,simulation analysis and experimental verification research methods,around the complex geometric characteristics of thin-walled blades,and expands on the changes in energy density,microstructure,and mechanical performance during the deposition process.The qualitative analysis and quantitative research.Finally,on the basis of process optimization,the forming of twisted blades with unequal widths was realized,and related accuracy analysis and performance testing of the formed blades were carried out.The specific research content of this article includes:(1)Explore the best parameter combination of single-channel deposition and multichannel overlap rate.Based on the results of the deposition image processing,the effects of laser power,scanning speed and powder feeding rate on the morphology of single-pass deposition layers were analyzed,and the nonlinear relationship between the width of the singlepass deposition path and process parameters was quantitatively fitted.Designed and completed multiple lap experiments,using the top surface flatness of the deposition layer as an evaluation index,and quantitatively compared the deposition morphology under different lap rate to obtain the optimal lap rate.(2)Established an energy density model for the laser-powder coupling distribution in the actual deposition process.Based on the physical premise of the change of laser focal plane and powder convergence point in the thin-wall forming process,a single-leaf hyperboloid is used to fit the laser beam,and a Gaussian heat source is used to simulate the heat flux density of any section along the beam propagation direction.At the same time,combined with the probability density distribution of the coaxial powder beam on the deposition plane with different defocusing amounts,the effective energy density model considering the laser-powder coupling is optimized,and the quantitative relationship between energy density,defocusing amount and heat distribution is analyzed.(3)The actual energy density change and the performance difference of the formed thin wall under different lifting conditions are studied.Through the analysis of the difference between the actual deposition height and the theoretical increase caused by the difference in the lifting amount,the measured values of the lifting variance,the width variance,and the top flatness are calculated,and the forming effect is quantitatively evaluated.Combined with the calculation results based on the energy density model,the influence of energy density on the microstructure in the vertical direction of the deposition layer is analyzed.In addition,the effects of energy density on the tensile properties of the sample in the horizontal and vertical directions are respectively explored.(4)The research and optimization of the forming process of complex geometric features have been completed,and the forming of the blade has been realized.The lifting model of inclined thin wall and twisted thin wall is established and the interlayer lap rate is derived.Combined with the experimental results,the maximum inclination angle,the maximum torsion angle and the corresponding minimum interlayer lap rate of thin-wall deposition are determined.Based on the above model calculation and experimental analysis,the torsion unequal width blades of two alloy materials of Inconel 718 and TC4 were formed,and the three-dimensional deviation measurement and organization of the formed blades were carried out,which proved the effectiveness of the forming process.